Scaling up your box jumps? Matt Blankenship builds a DIY extender to turn a 30-inch box into a 40.

Many CrossFit gyms use the Games-style 20 x 30 x 24 plyo boxes that are constructed to allow for 20-, 24- or 30-inch box jumps depending on how they’re set up. Smaller boxes are readily available and see plenty of use, but what do you do when you want to go higher than 30 inches?

Most of the time, the answer is to try to stack bumper plates on top of the box to achieve the desired height. While this can be an effective solution, it can also pose problems including the following:

It weakens the box. To get much of a height increase, you might have to stack several hundred pounds of weights on top of a wooden box.

It makes the box unstable. Stacking plates will immediately shift the center of gravity of the box and make it extremely top heavy. Also, the plates can move and shift.

It changes the shape of the box. Where he or she would be landing on a rectangular platform, the jumper is now forced to aim for a smaller, circular target. This forces the athlete to move the feet into a narrower, less stable position.

It’s possible that all these factors can be dealt with when going for single high jumps, but what about repeated jumps for practice or in a WOD? There is a better way, and it is safe, cost effective and relatively simple: an extension for the box.

I think it would be valuable to point out that you could build a box capable of multiple level increases by building your internal 2x lumber element out of smaller stock (i.e. 2x4s) and making several frames. This would give you the capability to increase height incrementally by 3.5 inches limited only by the height of your external box. Very good article. I plan on merging our two ideas. Thank you. (I'm a crossfitter and a carpenter by the way :-))

Robert, by all means, merge away. You might even consider using 2x3s for the stackable frames. I have found that they are plenty strong and are often better quality than many 2x4s. This would also allow you to adjust the height in smaller increments. .

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